Refrigeration equipment is used widely to preserve the quality and to extend the shelf-life of many commercially valuable products—principally food but also such items such as blood, plasma and other tissue. It is rare today to find a produce store of any size that does not have some refrigeration equipment. Generally, the sale of meat and dairy products without adequate refrigeration is prohibited by regulation. Refrigeration equipment may be located close to the origin of the foodstuff (be it a dairy, a slaughterhouse, packing or manufacturing plant) for temporary storage, during its transportation (on trucks, trains or ships), in warehouses or depots where it is again temporarily stored, and in retail outlets and restaurants where it is sold.
The most widely-used refrigeration systems rely on the cooling provided by an evaporator located within the space to be cooled or in thermal communication with the space to be cooled. This cooling is obtained by the rapid expansion of gas. A refrigerant gas is contained in a sealed conduit forming a closed loop. A compressor compresses the refrigerant in its gaseous phase into a condenser. The compression causes a heating of the refrigerant, and that heat is drawn away by a stream of air or water flowing over a heat exchanger associated with the condenser. Usually this loss of heat causes the refrigerant to liquefy. Liquid refrigerant is released through an expansion valve downstream of the condenser into an evaporator, in which the pressure is appreciably lower than that of the region upstream of the expansion valve. In the evaporator, vaporization of the liquid and expansion of the gas so produced occur. This expansion and vaporization require energy, which is taken as heat from the walls and surroundings of the evaporator, causing a cooling in the vicinity of the evaporator (including cooling of any chamber or the like with which the evaporator is in thermal communication). To facilitate heat exchange, the evaporator is typically provided with a heat exchanger and cooling fins, and a fan or the like is typically used to maintain a stream of air over the evaporator. The evaporator accepts heat from the air stream, reducing its temperature. The cool air so produced is circulated by the fan within the chamber to be cooled.
Many of the earliest refrigerators used ammonia as the refrigerant. This choice was thermally effective, but highly toxic. More recently some members of the class of chlorinated flourocarbons (“CFCs”), such as dichloroflouromethane CCl2F2, have been used as they are odourless and non-toxic in moderate quantities. However, CFCs have been found to be deleterious to the environment, with particularly troubling effects on the ozone layer of the atmosphere. More recently CFCs have been replaced with hydrocarbons such as cyclopentane.
The evaporator may cool sufficiently to form ice on its surface and, over time, ice build-up can become a problem. The ice acts as an insulator, with the consequence that the evaporator's heat exchanger may become blocked so that air cannot flow effectively over its surface. Periodically it is necessary to defrost the evaporator to remove the coating of ice. This is usually done using a defroster in the vicinity of the evaporator that employs a heater, hot gas or hot water to remove the ice build-up.
Typically, refrigeration systems are controlled either by one or more thermostats located in the space to be cooled or by a sensor measuring the refrigerant pressure in the evaporator. When one or more of these sensors indicates that the temperature or evaporator pressure has risen sufficiently to exceed an appropriate selected upper threshold, the compressor is activated, and cooling begins. Cooling continues until either a selected lower temperature limit is reached or the pressure in the evaporator has fallen sufficiently, at which time the compressor is turned off. Ideally, the compressor's ON and OFF cycles are regular and predictable (except of course when the refrigerator is opened to permit insertion or removal of its contents).
The impaired performance of a refrigeration unit is costly. Food that is not kept within an optimal temperature range loses its quality and can spoil; if it can still be sold, it typically commands a lower price. Taking a refrigeration unit off-line to be repaired means that there is less space available for the storage or display of produce. With a smaller variety of produce on display, sales are likely to be reduced. Typically, the value of the produce in even a modest cooler of a small grocery store is measured in the thousands of dollars; the value of cooled produce in a larger supermarket can be in the hundreds of thousands of dollars.
Refrigeration systems use energy to provide cooling. If they are working inefficiently, there is an additional cost for the energy consumed.
Problems with refrigeration equipment that lead to faults or failure include the following:                Leaks of the refrigerant. The piping and seals that contain the refrigerant are subject to vibration stresses that eventually can cause cracking or rupture of the metal. Corrosion from oxidation or the effects of acid impurities can also cause leaks.        Heat exchangers used in the condenser and in the evaporator are designed to present a large surface area and to be made of thin metal for better heat conduction. This makes them fragile and prone to breaks if they are mishandled.        A compressor typically has a pump driven by an electric motor. Both the pump and the motor have mechanical parts including valves, bearings, seals and brushes, all of which wear with use over time, leading to possible breakdown.        Fans are frequently used to maintain streams of air over the condenser (to remove heat) or over the evaporator (to distribute cold air). The fans have mechanical and electrical parts that can wear and ultimately fail.        The heat exchangers can become coated with dust, dirt or ice or their heat-exchange surfaces blocked with items such as plastic bags or paper.        The power supply may be subject to voltage spikes, may suffer periods of low voltage, be interrupted or overloaded.        The defroster may lose power or, if the defroster is of the hot-gas type, the solenoid may seize, and the defroster will be unable to remove ice build-up from the evaporator.        
The early detection of fault conditions can mean the avoidance of more costly repairs. Quite commonly, electromechanical devices such as pumps and fans show signs of poor performance well in advance of failure. Being able to spot and correct a deteriorating situation before it becomes critical can save considerable down time and expense.
For example, a slow leak of refrigerant will probably produce a predictable pattern of system operation. At first, with less refrigerant to work with, the compressor will have to run for a longer on-cycle to achieve an equivalent cooling effect. If the compressor is regulated by a thermostat within the refrigerated compartment, the length of the on-cycles will continue to increase until a point is reached where the compressor does not shut off at all. Alternatively, if the compressor is regulated by the pressure at its intake, the drop in pressure from the loss of refrigerant will cause the compressor to be shut off early, typically just after it has started up. This is often referred to as “short-cycling”. In some cases, the protective circuitry of the compressor will ensure that the compressor is shut down, sometimes without any warning. This may protect the compressor from damage but may jeopardize the food stored in the refrigerated compartment. Another problem may be that the compressor refuses to start. Diagnosing why this is so is greatly simplified if the service technician has access to the recent history of the compressor's operation. Further, if the length of the on-cycle can be routinely monitored, the problem may be detected before it has become critical.
As a further example, an electromechanical device like a compressor has bearings, bushings and its drive motor has brushes. These are all parts subject to wear. Over a period of time there will be increased resistance caused by friction, particularly if lubrication has been inadequate for any appreciable time. This resistance can be readily observed as a persistently increasing current drawn by the compressor during operation and by a longer period of high current draw during start-up. Knowing well in advance that the compressor is beginning to have trouble is of great value as it enables operators of the equipment to plan for a compressor replacement at a convenient time and avoid a complete breakdown.
There is a considerable variation in the operating environment of refrigeration equipment; it is difficult to predict what are normal ranges for various operating parameters of the equipment. Variations in performance are to be expected—for example, ambient temperature, number of people in the vicinity, the mass of stored material in the refrigerator or freezer, etc. will vary appreciably from day to day and sometimes from hour to hour. There may be variations in the power supply voltage. The quality of wiring and connections will vary from installation to installation. And there is typically significant variation in the number of times in a day the cooling/storage compartment is opened, and for how long. The situation is further complicated as some enterprises will have a number of coolers, chillers and freezers operating.
The diagnosis of problem situations is normally a matter that needs attention from a qualified technician and is not usually addressed by staff untrained in refrigeration. To avoid the risk of lengthy down time, such technical help may be required 24 hours per day and is sometimes not to be found close at hand. This can cause the following types of difficulties:                The technician may be called in when he is not needed. For example, a warning that the compressor has been running for longer than usual may simply be due to the fact that the freezer door has been left open.        The technician may not be advised correctly or be advised too late of the problem situation. In either situation, the technician may not be able to respond in time to prevent a critical situation.        The technician may not have available sufficient information to make an accurate diagnosis of the problem. If he is lucky, upon arrival, the technician may find that the refrigeration unit still functions and that some sensor information is available. But the system may by the time the technician arrives have reached a critical situation and may have had to be shut down, either manually or by protective circuitry. When this is the case, the technician may have limited information available from which to diagnose the problem. In some circumstances attempts at diagnosis can lead to further damage. With inadequate information, repairs are often more costly as components that are working properly are sometimes needlessly replaced in an attempt to fix the problem.        
Many types of refrigeration monitoring equipment have been devised previously. However, such equipment has typically dealt with some but not all important aspects of the problems facing service technicians. In particular:    (1) Designs of prior monitoring equipment typically do not permit a comparison of pre-failure equipment performance with the problem performance leading up to the failure. Prior designs typically do not allow for the recording of operational parameters as historical time series for monitoring purposes. A “time series”, as used herein, means a series of values of a parameter obtained and recorded at successive times, usually with equal intervals between the times.            U.S. Pat. No. 5,209,076 (Kauffman et al., 1993) teaches the measurement of a selection of operational parameters and comments on the value of their collection over an extended period of time. U.S. Pat. No. 4,090,371 (Keane, 1978) teaches apparatus for monitoring the characteristics of lubricating oil at significant points within the compressor and points out that recording the precursor history prior to malfunction can provide diagnostic information for speedy repair. However, in neither of these patents is there any teaching in any enabling disclosure of the details of how the collection and recording of useful historic data might be accomplished.            (2) Prior teachings typically fail to take into account the idiosyncratic nature of the components installed in any particular refrigeration unit. For example, consider the problem faced by an engineer or technician to determine a reasonable value for the average duration of the compressor on-cycle. There are many manufacturers of compressors, each of whom typically sells many models of compressor. Further, the performance of any particular compressor, even of the same make and model, varies. Once a compressor has been selected, the duration of the on-cycle will depend on many other factors—such as the other components installed, the size of the refrigeration compartment, the amount of insulation installed, ambient temperature, and how much unrefrigerated material is within the refrigeration unit. Typically, this has meant that reference values for operational parameters have been selected with a good measure of guesswork, or by way of averaging over a large number of units, and that historical parameter values recorded as a time series have not been used.    (3) The prior art typically does not disclose adequate means for providing supporting data to a service technician to improve his ability to diagnose a problem. In some cases, refrigeration monitoring equipment does nothing more than shut down equipment that may be suffering from some problem within a selected set of problems. In a few cases, the service technician can find out which operational parameter has a value indicating a fault. Prior monitoring apparatus typically does not include means for notifying the technician of possible alternative causes for the reported problem.    (4) Frequently, refrigeration monitoring equipment includes checks on the values of operational parameters such as refrigerant pressure, the temperature in the refrigerated compartment and the currents drawn by and voltages applied to electrical equipment. However, few designs of prior monitoring equipment take into account all of the principal problem types with which a technician must cope. For example, prior monitoring devices typically do not include means for comparing the duration of the compressor's on- and off-cycles against normal values.            In the prior art, a number of issued patents address the problem of detecting leaking refrigerant. A common solution to this problem is to detect the presence of the refrigerant, or a tracer chemical mixed with the refrigerant, as it leaks into the air surrounding the refrigeration unit. An example of this approach is set out in U.S. Pat. No. 6,131,636 (Singh et al., 2000) in which the inventors teach the use of dye that fluoresces under ultraviolet light.        Alternatively, low refrigerant charge can be detected by observing the pressure either at the suction side of the compressor (as in U.S. Pat. No. 5,481,884 Scoccia, 1996) or at the discharge side of the compressor (as in U.S. Pat. No. 5,586,445 Bessler). However, the pressure of the refrigerant needs to be measured after the system has had a chance to stabilize, and this is difficult to determine without an effective record of the operating parameters each as a time series. For example, U.S. Pat. No. 5,044,168 (Wycoff 1991), discloses a method for detecting low refrigerant levels by comparing the suction pressure and the discharge pressure while the compressor is idle during a defrost cycle.        U.S. Pat. No. 5,934,087 (Watanabe et al., 1999) teaches the use of two temperature sensors and a means for measuring the cumulative running time of the compressor to judge a refrigerant leak. This approach suffers from the drawback that the monitor will report a refrigeration leak only once the loss of refrigerant is almost complete and the compressor is running for an extended on-cycle. This approach may provide a correct diagnosis of the problem; however, diagnosis may come too late, in that by the time such a report is received, the temperature in the refrigerated compartment may have risen and jeopardized the quality of its contents. Although Watanabe recognizes the importance of the duration of the on-cycle, the apparatus disclosed does not record the compressor's current drawn as a time series, and comparisons of on-cycles over a period of time are not possible. Further there is no indication how reference values are to be determined.        U.S. Pat. No. 6,354,093 B2 (Davis et al., 2002) teaches the measurement of the most recent compressor running time, the evaporator coil temperature, last door-alarm time, last defrost time period, door-closed time period, and discharge-line temperature, to determine when a defrost operation is required and to monitor for condenser clogging and refrigerant leaks. The efficacy of the algorithms presented in Davis rely on having threshold values available for all of the operational parameters, but Davis provides no enabling disclosure on how these values are to be chosen. Further, the algorithms presented do not take into account all the fault events that could occur. For example, the claimed control system fails to detect the following fault situation:                    the defrost operation is not overdue (that is LDTP<TLDTP);            the compressor running time (CRT) exceeds the desired threshold value (TRT);            the discharge line temperature (DLT) is within reasonable bounds;            the reason for the long CRT value is due, not to the loss of refrigerant or the clogging of the condenser, but rather to the malfunctioning of the compressor.                        U.S. Pat. No. 4,553,400 and 4,612,775 (Branz, 1985 and 1986) disclose a selection of sensors combined with a digital display to monitor a section of operating parameters, including a direct measurement of the refrigerant level.        A number of patents deal with the detection of problems with the compressor. In U.S. Pat. No. 4,090,371 (Keane, 1978) the inventor teaches apparatus for monitoring the nature of the lubricating oil at significant points within the compressor. Keane makes the point that recording the performance history prior to malfunction can provide diagnostic information for speedy repair, but provides no disclosure of how this might be done.        Other prior patents focus on different items of equipment or specific narrow methodology for dealing with a small number of faults but not all of the more common ones. For example, U.S. Pat. No. 5,009,075 (Okoren, 1991) describes a fault determination method for refrigeration units that incorporate an electronic expansion valve and electronic controller. In U.S. Pat. No. 6,205,798 B1 (Porter et al., 2001) the inventor teaches a method for the automated detection of leaks through the compressor. U.S. Pat. No. 4,848,096 (Funahashi et al., 1989) discloses means to make an automatic diagnosis of the pressure sensors as measured on the input and output sides of the compressor without disassembly of the compressor.        In U.S. Pat. No. 6,332,327 B1 (Street et al., 2001), the inventors disclose apparatus and methods particularly suited to control refrigeration equipment in large supermarkets. Typically such equipment makes use of multiple compressors, each of which has a number of sensors. The inventors disclose a safety and control module incorporating a bus for communication between modules to simplify the wiring for communication between the system's active components. This makes it possible to distribute the intelligence required to operate multiplexed compressors.            (5) The prior art includes reference to the use of telecommunication equipment to notify a service technician of a problem. For example, Kauffmann (supra) teaches the desirability of automatic notification of a service technician over a telephone line. However, Kaufmann fails to provide any disclosure detailing how this might be carried out.            U.S. Pat. No. 5,136,281 (Bonaquist, 1992) discloses a “Monitor for remote alarm transmission”.        U.S. Pat. No. 4,482,785 (Finnegan et al.) discloses means to alert technicians by telephone of any unusual temperature detected within a freezer compartment.            (6) The prior art typically discloses no means for a service technician to connect a monitor electronically to refrigeration equipment from a remote location and to access historical and real-time data representing the values of significant operational parameters.